Cyclopentadienyl manganese compounds are excellent antiknocks in gasoline used to operate internal combustion engines. These manganese compounds have proved to be especially beneficial in solving some of the problems present when low-lead or lead-free gasolines are used with internal combustion engines. Use of such compounds as antiknocks is described in U.S. Pat. No. 2,818,417; U.S. Pat. No. 2,839,552; and U.S. Pat. No. 3,127,351, incorporated herein by reference. Not only are these compounds effective antiknock compounds, but it has also been found that they do not adversely affect the activity of oxidation metal catalysts used to decrease the amount of undesirable constituents in engine exhaust gas. Under some operating conditions it has been found that, although the manganese antiknocks do not lessen the activity of the exhaust gas catalyst, they can interact in some manner at the surface of the catalyst bed leading to a reduction in the size of the openings into the bed thereby causing an increase in exhaust backpressure and a decrease in the effective life of said catalysts. The present invention provides a simple effective means of alleviating this problem.
It has been previously suggested that the addition of triethyl citrate to gasoline mixes containing organomanganese antiknocks tends to reduce catalyst plugging. The use of triethyl citrate, however, has proved to be of rather limited success in reducing the plugging problem, especially at higher temperatures. Also, application Ser. No. 483,642, filed June 27, 1974, now U.S. Pat. No. 3,926,581 discloses the addition of the esters and other fuel soluble derivatives of nitrilotriacetic acid to gasoline mixes containing organomanganese antiknocks to reduce catalyst plugging.